Marine engines typically draw water from the operating environment to perform heat exchange with elements of a watercraft. For example, sea water can be drawn in via a seacock in the hull of a watercraft to cool engine components and provide air conditioning of the watercraft quarters. To create a sufficient flow of water for such applications, an engine crankshaft drives a raw water pump of an open loop system mounted on or near the engine to pump water directly through water jackets of the engine or through a heat exchanger including piping of a closed loop cooling system.